Structure-from-motion based on information at surface boundaries

Existing computational models of structurefrom-motion — the appearance of three-dimensional motion generated by moving two-dimensional patterns — are all based on variations of optical flow or feature point correspondence within the interior of single objects. Three separate phenomena provide strong evidence that in human vision, structure-from-motion is significantly affected by surface boundary cues. In the first, a rotating cylinder is seen, though no variation in optical flow exists across the apparent cylinder. In the second, the shape of the bounding contour of a moving pattern dominates the actual differential motion within the pattern. In the third, the appearance of independently moving objects changes significantly when the boundary between them becomes indistinct. We describe a simple computational model sufficient to account for these effects. The model is based on qualitative constraints relating possible object motions to patterns of flow, together with an understanding of the patterns of flow that can be discriminated in practice.     

Somatic embryogenesis and plant regeneration from immature embryos of western larch

Somatic embryogenesis was initiated from immature embryos of western larch (Larix occidentalis Nutt.) on media containing 2,4-dichlorophenoxyacetic acid and N6- benzyladenine. The effects of explant type and ammonium nitrate and glutamine concentrations on initiation were tested. Although 21–93% of explants rendered cultures in various experiments, only 3% yielded sustainable embryogenic lines. Excised embryos at the early cotyledonary stage were optimal for initiation. Maturation of somatic embryos was promoted by abscisic acid. Response to abscisic acid concentrations and duration of exposure to abscisic acid varied with genotype. Maximal results were obtained with 0.025 M abscisic acid for 1 to 2 weeks followed by individual culture on medium without growth regulators. Mature somatic embryos developed into shoots with roots. Plantlets have been established in peat.Abbreviations 2,4-D 2,4-dichlorophenoxyacetic acid - BA N⁶-benzyladenine - IBA indole-3-butyric acid - ABA abscisic acid     

Expert systems in histopathology. IV. The management of uncertainty.

Expert systems deal with data that are categorical and conceptual, that represent elements of fuzzy sets and that often, by themselves, do not allow an unequivocal decision. The management of uncertainty in expert systems thus becomes a crucial issue. It involves defining measures of uncertainty and procedures for combining accumulating evidence in a manner that properly considers the dependence structure of diagnostic clues. Probability theory offers valuable procedures for uncertainty assessment; however, their practical application in the domain of quantitative histopathology and histopathologic diagnosis can be problematic.     

The organotypic culture of human skin keratinocytes and fibroblasts to achieve form and function

We describe an organotypic model of human skin comprised of a stratified layer of human epidermal keratinocytes and dermal fibroblasts within a contracted collagen lattice. Feasible and reproducible production of the skin construct has required the use of traditional as well as specialized culture techniques. The configuration of the construct has been engineered to maintain polarity and permit extended culture at the air-liquid interface. Morphological, biochemical and kinetic parameters were assessed and functional assays were performed to determine the degree of similarity to human skin. Light and ultrastructural morphology of the epidermis closely resembled human skin. The immunocytochemical localization of a number of differentiation markers and extracellular matrix proteins was also similar to human skin. Kinetic data showed a transition of the epidermal layer to a morein vivo-like growth rate during the development of the construct at the air-liquid interface. The barrier properties of the construct also increased with time reaching a permeability to water of less than 2%·h after approximately 2 weeks at the air-liquid interface which is still on average 30-fold more water-permeable than normal human skin. The construct is currently used forin vitro research and testing and is also being tested in clinical applications.     

Cardiovascular actions of adenosines, but not adenosine receptors, differ in rat and guinea pig

This study compared the structure-activity relationships of 16 analogues at the A1 and A2 adenosine receptors (A1AR, A2AR) of rat and guinea pig. Radioligand binding studies revealed no marked differences in the affinities of each analogue at the A1AR of brain cortex or the A2AR of brain striatum. Bioassay employing Langendorff heart preparations showed that the guinea pig is more sensitive than the rat to A1AR-mediated slowing of conduction through the atrioventricular node and, in some instances, to A2AR-mediated coronary vasodilation. That difference could reflect factors such as receptor density or efficacy of coupling to effector systems.     

Effect of substrate on Ca2(+)-concentration required for activity of the Ca2(+)-dependent proteinases, mu- and m-calpain

The Ca2+ concentrations required for half-maximal activity of mu- and m-calpain purified from bovine skeletal muscle were tested using four different protein substrates and three different synthetic peptide substrates. Hammersten casein, the commonly used substrate for measuring mu- and m-calpain activity, required 2.5 microM Ca2+ for half-maximal activity of mu-calpain and 290 microM Ca2+ for half-maximal activity of m-calpain. When Hammersten casein was dialyzed against 8 M urea and 10 mM EDTA to remove all endogenous Ca2+, it required 1.9 and 290 microM Ca2+ for half-maximal activity of mu- and m-calpain, respectively. Rabbit skeletal muscle myofibrils and rabbit skeletal muscle troponin required 65 microM and 24 microM Ca2+ for half-maximal activity of mu-calpain and 380 microM and 580 microM Ca2+ for half-maximal activity of m-calpain, respectively. The three synthetic substrates tested, Suc-Leu-Tyr-MCA, Boc-Leu-Thr-Arg-MCA, and Suc-Leu-Leu-Val-Tyr-MCA, required 1.6 microM to 3.7 microM Ca2+ for half-maximal activity of mu-calpain and 200 to 560 microM Ca2+ for half-maximal activity of m-calpain.     

Properties and applications of human DNA repair genes

The importance of understanding DNA repair processes is discussed in terms of the origins of human cancer. Several human repair genes have been mapped to specific human chromosomes using somatic cell hybrids. It is noteworthy that 3 of these genes lie in the same region of chromosome 19: genes ERCC1 and ERCC2, which are involved in nucleotide excision repair, and XRCC1, which is involved in the repair of strand breaks. The genes XRCC1 and ERCC2 were cloned from cosmid libraries prepared from DNA transformants of the CHO mutants EM9 and UV5, respectively. Analysis of the cDNA sequence of ERCC2 showed that the protein encoded by this gene is highly homologous (73%) to the RAD3 repair protein in the yeast Saccharomyces cerevisiae. Thus, the known properties of RAD3 combined with the high homology provide the first insight about the biochemical role of a human repair protein involved in the incision step of nucleotide excision repair. So far XRCC1 is the only cloned mammalian gene involved in repairing damage from ionizing radiation. The UV5 mutant line was also applied to problems in environmental mutagenesis by introducing the mouse cytochrome P(3)450 (P450IA2 subfamily) gene for metabolic activation of aromatic amines. We show in a rapid differential cytotoxicity assay with 2 compounds found in cooked beef (IQ, 2-amino-3-methylimidazo[4,5-f]quinoline and PhIP, 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine) that this gene is efficiently expressed in the transformed UV5P3 cells. Reversion of the repair deficiency in these cells will give a matched pair of cell lines that are metabolically proficient and repair deficient. Such lines will provide a rapid assay for genotoxic heterocyclic amines requiring activation.     

The effect of established plants on recruitment in the annual forb Sinapis arvensis

Summary The germination response of Sinapis arvensis to the presence of established plants was investigated in a greenhouse experiment. Established conspecific and heterospecific plants were found to inhibit germination and reduce the probability of recruitment of those seeds that germinate. Established plants have no effect on seed mortality in the soil. Using a simple recruitment model, it is demonstrated that the combination of variance in germination time coupled with the interaction between buried seeds and established plants can generate density dependence. The implications of these results for community processes, such as succession, are discussed.     

Native root-nodule bacteria of traditional soybean-growing areas of northern Thailand

Over 1500 root-nodule bacteria were isolated from a range of uninoculated soybeans, and one cowpea, trap-hosts, sown in 1985 into traditional soybean-growing areas of soybean-growing areas of northern Thailand. Most isolates were slow-growing Bradyrhizobium japonicum. Using a modified bottle-jar technique, 586 of the isolates were tested with a range of soybean hosts and one cowpea host. The results indicated: